Method of producing toner for developing electrostatic images

Abstract

A method of producing a toner for developing electrostatic images includes Steps I to III is provided. The toner includes a toner matrix particle having a core-shell structure. The toner matrix particle includes a core particle including an amorphous resin A and a crystalline material, and a shell including an amorphous resin B. The shell includes a phase of the amorphous resin B that is not fused with the core particle at the interface. The amorphous resin A differs from the amorphous resin B.

What is claimed is: 
     
       1. A method of producing a toner for developing electrostatic images, the toner comprising a toner matrix particle having a core-shell structure, wherein
 the toner matrix particle comprising a core particle comprising an amorphous resin A and a crystalline material, and a shell comprising an amorphous resin B, 
 the shell comprising a phase of the amorphous resin B that is not fused with the core particle at the interface, and 
 the amorphous resin A differing from the amorphous resin B, the method comprising the steps of: 
 Step I) dispersing at least the amorphous resin A and the crystalline material in an aqueous medium to prepare a dispersion, and adjusting a temperature of the dispersion to be equal to or higher than (a glass transition temperature (T g-a ) of the amorphous resin A+10)° C. and equal to or lower than (a melting point (T m-c ) of the crystalline material+10)° C., to prepare a core particle dispersion through coagulation and coalescence of at least the amorphous resin A and the crystalline material; 
 Step II) cooling the core particle dispersion prepared in Step I to a temperature equal to or lower than the glass transition temperature (T g-a ) of the amorphous resin A; and 
 Step III) adjusting a temperature of the core particle dispersion to be equal to or higher than (the glass transition temperature (T g-a ) of the amorphous resin A+5)° C. and equal to or lower than (a glass transition temperature (T g-b ) of the amorphous resin B+3)° C. after Step II, and then adding a dispersion of the amorphous resin B to the core particle dispersion, 
 wherein Expressions 1 and 2 are satisfied in Step III:
     pH   b   ≤pH   a , and  Expression 1:
 
   2≤ pH   b ≤5  Expression 2:
 
 
 
       where pH a  represents the pH of the core particle dispersion at 25° C., and pH b  represents the pH of the dispersion of the amorphous resin B at 25° C. 
     
     
       2. The method according to  claim 1 , wherein the core particle dispersion cooled in Step II contains a core particle having a shape factor SF-2 of 105 to 140. 
     
     
       3. The method according to  claim 1 , wherein the amorphous resin B added in Step III is a particle having a volume median particle size of 30 to 300 rm. 
     
     
       4. The method according to  claim 1 , wherein the amorphous resin A is a styrene-acrylic resin, and the amorphous resin B is a polyester resin. 
     
     
       5. The method according to  claim 1 , wherein the amorphous resin A is a polyester resin, and the amorphous resin B is a styrene-acrylic resin. 
     
     
       6. The method according to  claim 4 , wherein the polyester resin is an amorphous polyester resin chemically bonded to a styrene-acrylic resin. 
     
     
       7. The method according to  claim 5 , wherein the polyester resin is an amorphous polyester resin chemically bonded to a styrene-acrylic resin. 
     
     
       8. The method according to  claim 6 , wherein the amorphous polyester resin chemically bonded to the styrene-acrylic resin has a styrene-acrylic content of 5 to 30 mass %. 
     
     
       9. The method according to  claim 7 , wherein the amorphous polyester resin chemically bonded to the styrene-acrylic resin has a styrene-acrylic content of 5 to 30 mass %. 
     
     
       10. The method according to  claim 1 , wherein the amorphous resin A has a glass transition temperature T g-a  of 35 to 50° C. 
     
     
       11. The method according to  claim 1 , wherein the amorphous resin B has a glass transition temperature T g-b  of 53 to 63° C. 
     
     
       12. The method according to  claim 1 , wherein the crystalline material comprises a crystalline resin or a release agent, if the crystalline material is the releasing agent then the releasing agent is one selected from the group consisting of a hydrocarbon wax and an ester wax, and the crystalline material has a melting point (T m-c ) equal to or higher than (a glass transition temperature (T g-b ) of the amorphous resin B+3)° C. 
     
     
       13. The method according to  claim 1 , wherein the ratio of the mass of the amorphous resin B added in Step III to the total mass of a binder resin is 5 to 35, and the binder resin comprises amorphous resin A and amorphous resin B.